The need to secure renewable sources of energy extends to what covers most of Earth's surface. Yet this potential, in the ocean, remains largely untapped. It consists of wind driven and tidal currents, thermal and salinity potentials, and waves. Of these, tidal power has distinct near-term economic potential because many concentrated electricity markets are in cities that developed in tideways. There is also long-recognized potential in near-shore ocean currents, such as the Florida Current. In the long-term, the eastward Pacific Equatorial Undercurrent (EUC) holds promise because its enormous scale spans one third of Earth's circumference. The EUC flows below both the overlying westward South Equatorial Current (SEC) and prevailing westward trade winds, so kinetic energy in these opposing flows may be captured without deep ocean mooring expense.
The objective of this invention is economic conversion of hydrokinetic energy from slow currents of less than 1.5 m/s. This will allow placement of tidal turbines outside of high speed “bottleneck” locations that constrain tidal flushing of inshore waters. Where urban demand for electricity is greatest, this environmental constraint is significant due to waste discharge and industrial legacy. To minimize this adverse effect, the present Electric Power Research Institute (EPRI) US resource assessment (Bedard et al., 2006) limits usable energy at such sites to only 15% of their full hydrokinetic potential. Targeting slow water energy therefore both alleviates the environmental impact and expands the usable resource. There is also considerable low energy density tidal resource in non-estuarine open continental shelf areas. Interestingly, Arbic and Garrett (2009) provide a resonance analysis of open ocean/continental shelf dynamics which shows that an increase in friction on a near-resonant shelf can lead to an increase in ocean tides, so targeted low energy density conversion may actually increase the tidal resource base. With respect to ocean current hydrokinetic potential, the Florida Atlantic University Florida Current survey (Driscoll et al. 2009) indicates annual average velocity less than 1.5 m/s at 50 m depth. Velocity in the core of the EUC is less than 1.25 m/s. Economic utilization of lower energy density resource will also expand run-of-river hydroelectric potential.